1. Field of the Invention
The present invention relates to a digital content downloading system in which digital content such as music files, video files, game software titles and so on are downloaded to a plurality of consumers through networks.
2. Description of Related Art
In a current business field using a communication network, the interest of people has been changed from “technology-oriented” to “service-oriented”. In particular, people have paid attention to the Asynchronous Transfer Mode (ATM) as a technique guaranteeing the Quality of Service (QOS) indicating the communication quality. In an ATM network with the appropriate network managing performance, various types of traffic such as the internet protocol (IP), frame relay and voice can be simultaneously processed, and the service quality for the digital content can be easily guaranteed. Therefore, the ATM network is expected as a strong tool for digital content delivery.
Also, if network managing functions of ATM networks are available, a business using networks can be easy by utilizing various QOS classes such as Variable Bit Rate (VBR), non-real time service classes and so on, which means the business becomes “service-quality oriented” instead of “technology-oriented”. For example, to provide a technology service for consumers, a highly-efficient QOS class can be used in stead of a simple class of Constant Bit Rate (CBR). The technology of the network management is not only used for the management of hardware such as routers, switches and so on, but also used as a means of “service management”.
This strict service management is feasible because the ATM network has a high-performance QOS managing capability. In the ATM networks, parameters such as a transfer bit rate (which is also called “bandwidth” in this technical field), a delay time, a delay variation, a burst size, a cell interval and a cell discard rate, thus the virtual circuit (VC) can be precisely established with QOS guarantee.
In ATM Forum, QOS characteristics of each virtual circuit are classified, and four service classes are defined. They are CBR class, real time VBR class, non-real time VBR class and available bit rate/unspecified bit rate (ABR/UBR) class.
As is described above, because the four service classes are provisioned in ATM networks, even though congestion occurs in one of the four service classes, the influence of the congestion to the other classes can be prevented. For example, even though the congestion of data traffic occurs in an ATM switch, voice or video traffic belonging to the CBR class can be stably transmitted.
Also, charging of downloading of digital content to each consumer using ATM networks has been studied. To maintain a competitive edge in public network services, a fixed charge for the digital content download is not proper, but a policy of determining a charge depending on a type of the digital content or a downloading quality of the digital content is desired. For example, in many proposals of charging mechanisms, it is applicable that a charge for a CBR service be higher than that for a best effort type UBR service. Also, it is proposed that a charge for digital content be selected by a time zone, or that a charge for the digital content be decided in proportion to a bandwidth used for downloading or a service time zone.
In these proposals, a consumer who downloads digital content is charged in dependence on not only types of the digital content such as music files, video files of a cinema or map and game software titles but also the quality or time of downloading digital content. Therefore, the charging mechanism depending on how to use networks is possible.
FIG. 18 is a diagram showing the configuration of an optical access network of a conventional digital content downloading system. This optical access network of the conventional digital content downloading system is disclosed in a paper of the Institute of Electronic Information and Communication Engineers, Vol. 82, No. 3, pp. 213–217, March, 1999. This type of the optical access network is generally called the Passive Optical Network (PON) system. The optical access network connects a plurality of consumers to a network operator through a subscriber line, which is an optical fiber.
In FIG. 18, each of reference numerals 1a, 1b and 1c indicates a consumer who purchases digital content, each of reference numerals 13a, 13b and 13c indicates an optical network unit (ONU) which denotes a terminator of a branch subscriber line formed of an optical fiber. The optical network units 13a, 13b and 13c are arranged in houses or offices of the consumers 1a, 1b and 1c. Also, a reference numeral 24 indicates an optical line terminator (OLT), arranged in an office of a network operator, for terminating a main subscriber line formed of an optical fiber, and a reference numeral 14 indicates a star coupler, connecting the branch subscriber lines to the main subscriber line, for distributing optical signals transmitting through the main subscriber line to the branch subscriber lines and transferring optical signals transmitting through each branch subscriber line to the main subscriber line.
In the above configuration, an operation of the optical access network (or the PON system) of the conventional digital content downloading system is described. Time slots of digital content to be transmitted from the optical line terminator 24 to the consumers 1a, 1b and 1c are distributed to the branch subscriber lines of the consumers 1a, 1b and 1c in the star coupler 14, and one time slot of the digital content to be transmitted to one consumer 1a, 1b or 1c is received in the corresponding optical network unit (ONU) 13a, 13b or 13c for each consumer.
FIG. 19 is a conceptual diagram of a bandwidth allocation in one subscriber line utilized in the PON system. As shown in FIG. 19, a total bandwidth (or a total data transfer rate) usable in one optical fiber forming the main subscriber line or each branch subscriber line is divided into a fixed bandwidth, which is allocated for a telephone, an integrated service digital network (ISDN) and so on, and a shared bandwidth fairly allocated for the consumers.
FIG. 20 is a diagram showing an allocation of the conventional bandwidth example for one subscriber line. The shared bandwidth of 10 Mb/s in one subscriber line is divided into a plurality of bandwidth fields allocated to a plurality of consumers. As shown in FIG. 20, the shared bandwidth is fairly shared among consumers on the same branch.
However, in the digital content downloading system using the conventional optical access network, if a large number of consumers 1a, 1b and 1c simultaneously download a large-capacity file of digital content, not only each consumer feels that a data transmission speed of the digital content is low, but also data loss may occur in the transmission of the digital content because the bandwidth allocated to each consumer is not sufficient. Re-transmission of the digital content is required in case of data loss. As a result, traffic of the subscriber line connected to the optical line terminator (OLT) of the network operator is increased more and more, which make other downloading of other consumers 1a, 1b and 1c fail. Usually, the number of consumers accommodated by one star coupler 14 is 16 to 32.
As shown in FIG. 20, a bandwidth usable for each consumer greatly changes when the number of consumers changes. Therefore, there is another drawback that it is difficult to predict a time period required to download the digital content to each consumer, so that operational efficiency of the digital content downloading may considerably becomes worse.